The present invention relates to a compound body composed of a metallic basic body and at least two superposed hard substance layers which contain no binder metals. Such a compound body is used as a part that is subject to wear and for machining metallic materials.
U.S. Pat. No. 3,837,896 discloses a compound body with an outer layer consisting of one or a plurality of extremely wear resistant deposits of Al.sub.2 O.sub.3 and/or ZrO.sub.2, and an inner layer consisting of one or a plurality of carbides and/or nitrides of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si, or B. In this compound body the inner layer has a thickness of 1 to 10.mu. while the outer layer has a thickness of 0.2 to 20.mu.. It has been found to be a drawback that pure oxide layers are very much subject to cracking and easily chip off.
German Offenlegungsschrift No. 2,233,699 discloses a method for increasing wear resistance of hard metal parts in which at least part of the surface of the hard metal part is provided with a coating up to a thickness of 50.mu. of at least one oxide, nitride or boride. This publication also proposes the application of a coating of a mixture or a combination of the above-mentioned compounds on the hard metal parts.